Thermal batteries are used in many military applications that have the potential for an immediate or sudden demand for electric power. The thermal batteries have proven to be essential for providing power for radar and electronic guidance, and are able to operate in the high spin and setback environment of artillery shells, and operate in the high shock experienced in an earth-penetrator weapon. They can remain in weapon systems for 25 years or more over a wide range of storage (−55° C. to 75° C.) without degradation, and should be hermetically sealed as the moisture and air degrade the battery significantly.
Thermal batteries are operated at temperatures between 350-550° C. with molten salt electrolyte. They are inactive at room temperature as the molten salt electrolyte is in a solid state bearing a low ionic conductivity for minimizing self discharge and degradation processes. This low conductivity phase of the electrolyte promotes the capability for this type of battery to have very long shelf life with practically no capacity fade, and then can be activated within less than one second. For battery activation, internal pyrotechnics are ignited that generate thermal energy to raise the battery internal temperature to the melting temperature of the electrolyte, thereby causing a large increase in its ionic conductivity thus allowing the battery to operate. The battery is active as long as the electrolyte is above its melting point (e.g., typically above 350° C.) and generates power as long as enough active mass is available for the charge transfer reaction.
Previously, the most advanced common configurations of thermal batteries feature lithium-silicon alloy powder as anode material, FeS2 as cathode material, and eutectic electrolyte such as LiCl—KCl or halide electrolyte mixture of LiCl—LiF—LiBr. The configurations operates at voltage less than 2 V and the capacity is limited, e.g., limited to 335 mAh/g for LiSi alloy-FeS2 redox couple. These configurations cannot meet the requirements of new applications that are demanding high power and energy density. The principal avenue for increasing thermal battery specific energy is to identify and develop new chemistry and electrode materials, which provide high power with single cell voltages>2.5 V. The combination of higher specific capacity and higher operating voltage translates directly to higher power density at the battery level. The battery materials should be environmentally friendly, and potentially inexpensive in large scale production. As lithium alloyed with silicon or aluminum or tin provides high capacity as the anode, the power and capacity of thermal battery depend upon the cathode material.
Therefore, it would be advantageous to have improved thermal batteries that overcome the shortcomings of prior thermal batteries.